Lathe enlarging of mold?

[Canuck Bob]

I have a nice little Southbend lathe and am wondering what is involved in learning to enlarge the mold?

Any links or advice possible would be appreciated.

Do you index with a 4 jaw or on a clamp plate?

Is the tool a single tip or ground for cutting all grooves at once?

I will be destroying some LEE molds for practice.

[Casting Timmy]

There was a nice article in the fouling shot an issue or two ago about how to open up the driving bands on a mold using a drill press. He woudl use something like a key way cutter and adjust it height wise to correctly hit the driving band he wanted to enlarge. Then with the drill press running slowly he would close the mold on the cutter and then turn off the drill and let it stop spinning before opening hte mold.

Some people cast bullets and open the mold a little by using the cast bullet with valve grinding compound to open the mold.

As for a 4jaw or clamping, I woudl say it depends on what you have and the size of the mold. If I was to do a 2 cavity, I think I would rubber band the mold together real tight and then use my tail stock in the cavity I wanted to modify to roughly center me up on the 4 jaw. The use your favorite method to get it perfectly centered in the 4 jaw.

Hopefully some of this helps you out a little.

[Southron Sanders]

No need to destroy those Lee moulds! I am assuming you have a 4 jaw chuck.

[1] What you need to do is to "Center" your mould in the 4 jaw chuck by centering off of the bullet cavity and NOT the flats of the mould block.

[2] What you want to do is enlarge your mould's driving bands so much. You can use a single point tool or make up your on "Form Cutting Tool" out of High Speed Steel.

[3] When enlarging your cavity, just keep in mind that you must go slowly. It is always easier to remove metal than add it back later!

WARNING-If you make your own "Form Tool" the next thing you will want to do is design and make up some custom moulds for yourself and friends. Proceed carefully, it is addictive!

Just keep in mind that with a little care you can make up a precision bullet mould that is probably better than any you can buy!

GOOD LUCK

[Canuck Bob]

Thanks guys, a bit tongue in cheek re the destroying molds.

I was originally thinking indexing off the cavity then cutting. As far as making molds I don't see it. Modding them is a different thing though.

There are so many undersized molds that I'm hoping for a deal on a couple. Also my shooting will be focused on plain base for awhile so removing the GC flange is interesting as well. Maybe if I can do this I'll tackle a paper patch mod.

[Buckshot]

..............Canuck Bob, Using either a 4 jaw independant chuck or a faceplate will work. The thing that is the same is to center up the cavity to the spindle's axis.

http://www.fototime.com/2E52E1F832F7ACF/standard.jpg

Something you can't help, but may open your eyes is to fully check out a set of mould blocks and the cavity(ies) it contains. It's can be a real edjumacashun:shock:

http://www.fototime.com/4E82C710D2AEAC9/standard.jpg

A setup in the 4 jaw. You'll invariably get a bit of a 'Bounce' across the parting lines. Say your TI is set on zero (using more then a .0005" indicating TI is a REAL headache) transitioning from one block half to another for example you might go from the .0000 to an indicated -.0015". Continueing to rotate the chuck 180º to the other line, if it goes from the -.0015 back to the .0000 you're gold. That is assuming that both the readings 90º perpendicular to the parting line indicate .0000.

If your TI has the reach and you were reading on the base, move as deep into the cavity as you can to read on another lube groove. If you have looked at a few moulds and their cavities on a surface plate, and indicating the same places in the cavity back and forth between the 2 blocks, it will ease your mind as to what you're seeing when trying to indicate the blocks in a 4 jaw OR on a faceplate as it rotates around the tip of the TI. Or at least you'll understand WHY you're seeing what you're seeing!

My point for bringing up the surfaceplate and checking a few moulds is merely a way to show that a lot of times thay aren't what a person would think, and the accuracy we DO get shooting boolits from those moulds is a cause for wonderment.

http://www.fototime.com/EC6E32186093ED1/standard.jpg

A mould setup in a toolmaker's vise on a faceplate. Another option is to use small angle plates. If you plan on using the surface plate and angle plates a lot for this type stuff, drill and tap a couple holes in the upright face of one of the angle plates. You can position the blocks against the face of the opposite angle plate. Then position the second angle plate up against the mould blocks, and snug it to the faceplate. Now thread in a bolt with a nut to lock it, through each of those 2 holes you'd D&T'd, to bear against the side of mould blocks. Probably be a good idea to have a couple brass, alum, or steel pads between those bolts and the blocks to prevent marring.

http://www.fototime.com/B14C8C7293C3501/standard.jpg

This is a Lyman 12 ga slug mould a person wanted drive bands cut into to open it up a bit, and to use in a rifled barrel. It was done in a 4 jaw. I had to grind a tool (form tool) to cut the drive bands. A couple VERY important things to remember, and the first is that there is NO substitute for mass and rigidity. In this case the tool had to stickout far enough to reach into the mould though the HB pin hole, PLUS enough extra length to reach the position of the top drive band.

Another thing to remember is that the wider the cutting surface of your tool, the more likely it is to chatter, unless your cuts are correspondingly lite. Boiled down to the basics you want the tool to be as fat as possible, to be as short as possible (least 'stickout'), and the cutting edge width to be as narrow as possible. My lathe does not have a digital readout, so those drivebands were cut using a dial indicator (DI) reading on the carriage for infeed, and one set on the compound for feeding out (away from the spindle's axis).

Once the tool entered the HB hole of that mould I couldn't see anything at all that was happening, and had to rely entirely on those 2 DI's. The state of anticipation I was in aduring that op defies description. I don't really care to ever have to do that again[smilie=l: Compared to this, boring out GC shanks or BB's is a snap! Anyway it's all a lot of application of simple common sense. Some of the best boring, and form tools come in the form of HSS drill or reamer blanks.

................Buckshot

[Southron Sanders]

Dear Canuck Bob:

Buckshot knows what he is writing about. I was having trouble making a Spoon for mould making and Buckshot told me what I needed to do.

I followed his instructions to the letter and everything worked out beautifully. I am still very grateful to him for his expert advice. So, you can't go wrong following Buckshot's instructions!

[Canuck Bob]

Thank you buckshot.

I got a ton of healing time till Christmas and will be tackling this soon as I fine tune my lathe. I once worked as a lathe operator in a Timken Bearing tool room. I just made the tools for heat treating before the real machinists ground them to optical tolerances. They were a fussy bunch though and I was challenged and scolded often. Asking them to grind 2 thou to spec might as well been a quarter inch. I learned to keep my tolerances tight, the steel cool, and not to stack.

Glad to hear there are some guys left using dials to index. The only thing digital in my shop is the radio, I think.